The invention relates to a device for controlling the temperature of substrates in a substrate treatment installation, in which a substrate can be guided in the longitudinal extension of the substrate treatment installation in a substrate transport plane within a vacuum chamber past a treatment device.
Treatment devices are understood in this case as coating devices, such as vapor deposition or magnetron devices, but also temperature treatment devices, sputtering and etching devices and the like.
During the treatment of substrates in such substrate treatment installations, heating devices are used both for heating substrates to the temperature required for the process in order to obtain the desired properties, and for maintaining the substrate temperature while the substrate passes through the process of the treatment device.
The known devices for heating substrates in substrate treatment installations substantially consist of heating elements, radiation protective shields, and a baseplate on which the heating elements and radiation shields are mounted. The baseplate can be embodied in cooled fashion.
Alongside the heating of the substrate, it may be necessary to maintain the temperature of the substrate between two process locations or else to increase the substrate temperature.
They can be very different types of processes:
Heat treatments: maintaining a specific temperature/time regime in a vacuum or under defined process gas conditions.
Coating devices: Maintaining the temperature required for coating in particular at the process location, but also possibly in the region between different process locations e.g. in a substrate treatment installation designed as a continuous installation, if necessary for obtaining layer properties.
One problem when designing the heating is that the treatment devices themselves can constitute considerable heat sources. This is the case for example at process locations such as magnetron sputtering, vapor deposition, etc. Therefore, in substrate treatment installations designed as continuous installations, undesirable heating of the substrate can occur depending on the specific heat capacity of the substrate, transport speed and thermal power input from the substrate treatment devices. In principle, that can be combated by reducing the power of the heating devices behind the substrate or switching them off.
In the case of high heat input into the substrate through the treatment devices, it can furthermore become necessary to dissipate excess heat via the substrate rear side by means of emission. In a vacuum, this procedure is possible only within the limits set by the emission power on account of the great dependence on temperature. If e.g. the desired substrate temperature is 300° C., under corresponding preconditions an emission power of approximately 5 kW/m2 cannot be exceeded. If the heat inputs from the treatment devices exceed this power, substrate heating has to be accepted.
Depending on substrate temperature, the theoretically possible emission powers are considerably above that at relatively high substrate temperatures.
In substrate treatment installations which operate at relatively high process gas pressures, heat conduction by the process gas is increasingly manifested. That can be exploited by the substrate rear side being brought into thermal contact with components such as rollers, for example. The thermal contact is realized by the heat-conducting process gas. Substrate and component which can be temperature-regulated can be in mechanical contact, although the mechanical contact is not necessary depending on the desired heat dissipation, provided that the gap dimension between substrate rear side and component is correspondingly adapted.
In the case of the steady-state heating of a substrate, in part rapid heating to the temperature required for the subsequent process is desired. A correspondingly dimensioned heating system can achieve this objective. In the case of continuous installations, almost the entire cycle time is generally available for this purpose. Substrate by substrate is brought to process temperature in this way, the heated substrate is removed and moved in the direction of the process, and the chamber that has become free receives the next substrate for heating.
However, there may also be the requirement, for instance for the processing of individual substrates, not to remove the substrate from the heating chamber at high speed and feed it to the process. Rather, e.g. for the case where the process chamber directly adjoins the heater chamber, it may be necessary not to remove the substrate at high speed from the heating chamber, but rather to lead it out at a comparatively low process speed. For this operating case, although a heating system as described above can enable the substrate to be rapidly heated, the type of heating system has the disadvantage that the heating itself can have comparatively considerable heat capacities, such that the temperature of the substrate after the heating has been switched off after the desired substrate temperature has been attained can overshoot considerably depending on the specific relationships. By suitably throttling or else switching off the heating system before the desired substrate temperature is attained, although the heat stored in the heaters and radiation shields can be utilized for subsequent heating, such that the substrate temperature is attained without overshooting, these compensation processes can take up considerable amounts of time and are therefore unacceptable.